The present invention relates to an improved electric indicator system for a field or court and ball game, and more particularly to an electric circuit system for determining when struck balls fall outside a field or court, such as a tennis court. It is within the scope of the present invention to utilize the present system in other types of games in which the playing area is within defined boundaries.
As will be hereinafter described, the present invention also represents a specific improvement over that claimed in my earlier issued U.S. Pat. No. 3,883,860 in that it is specifically directed to use on tennis courts having a "skidding" type surface such as clay or wood.
A principal object of the present invention is to provide a system in which players, spectators and umpires are able to determine accurately by visual or audio means, or both, whether or not a ball drops, i.e. hits the ground, outside the designated playing area without having touched any part of the playing area. It is another major object of the present invention to render unnecessary the use of linesmen at tennis matches. A further object of the present invention is to provide an electric indicator and warning system for court games which is relatively easy to install, instantaneous in response, inexpensive to manufacture and will not tend to distract the players while playing the game.
The need for an improved method of determining which tennis balls are "out" and which are still "in play" stems entirely from the difficulty for the human eye of a player, linesman or umpire to infallibly perceive whether a "close" ball is truly an "out ball", or whether the ball has touched the ground inside a line, or whether the ball has touched a line no matter how slightly, and therefore is an "in-bounds" ball and still in play. A person can usually, without danger of error, recognize an "out ball" touching the ground approximately an inch or more outside the line in question. It is a principal object of the present invention, therefore, to ensure that balls touching the ground on the outside of, but in close proximity to a line, xan immediately, automatically and infallibly be identified as being out, thereby terminating the point. It is another principal object of the present invention to prevent identifying a ball which has touched a line, and therefore is still in play, as an "out ball".
The problem of erroneous line "calls" in even the most important matches using experienced linesmen is a serious one. This problem usually arises with respect to either (a) those "out balls" that are very close to a boundary line, i.e. those that touch the ground within approximately one inch from the outside edge of the line, or (b) those close balls that actually remain in play, i.e. those balls that are not actually out, but have touched a line and are erroneously identified as "out balls". It is estimated that elimination of these two types of erroneous "calls", according to the present invention, will prevent more than 95% of the errors that are made. It also is estimated that in a "three out of five set" championship match, there occur less than ten questionable or erroneous "calls" and that the present invention will reduce the number of erroneous cells to 0-1 per match.
My earlier U.S. Pat. No. 3,883,860 pertains to an electric circuit and indicator system for a court game, such as tennis, using conductive elements on both the ball and outside the court playing area to activate a visual and audible indicator when the ball drops outside of the playing area. My earlier patent may enable a better understanding of the present invention and, to the extent necessary, such earlier patent is hereby incorporated by reference. Said patent eliminates by far the largest number of erroneous calls in tennis games played on such surfaces as cement, asphalt, composition, carpet and plastic surfaces made of extruded films or poured rubber and synthetic composites having a rough or textured surface and which do not have any loose sand, powder or other granulated material exposed on the surface.
I have now discovered, however, that the said system of U.S. Pat. No. 3,883,860 is less effective on tennis courts having loosely distributed material on its upper surface such as clay courts and also on tennis courts having very smooth surfaces such as wood. For instance, clay courts, having loosely distributed sand or crushed gravel on their surface, and wood courts, which frequently are lacquered, cause a tennis ball striking the playing surface to skid following the first impact. On clay courts, the length of the skid mark can easily be measured as it is often clearly visible and the overall length of such skid marks measured in the direction of the flight of the ball sometimes is more than four inches. This means that, following the first contact with the ground, the ball skids for a distance which is a multiple of the diameter of the area of first contact between the ball and the ground.
This phenomenon results in possible erroneous indicating by the system described in U.S. Pat. No. 3,883,860 with respect to surfaces which permit some or extensive skidding of the ball. These erroneous "calls" are caused by the ball closing the circuit described in the said U.S. Pat. No. 3,883,860 and activating the indicator after having struck the line which forms part of the playing area (it therefore being an "in ball") and skidding into contact with the conductive strips located outside the line. As a ball having struck any part of the playing area is still in play, the closing of the circuit of U.S. Pat. No. 3,883,860 by such an "in-play" ball, on a clay court would erroneously indicate an "out ball". By means of the present invention, this erroneous indication is avoided.
While the system described in U.S. Pat. No. 3,883,860 is very suitable and efficacious for play on "non-skid" surfaces, it is less so for "skid" surfaces, even though still far superior in results compared to play on courts not equipped with the said system. The present invention reduces the incidence of erroneous "calls" on those surfaces which permit a struck ball to touch a line and then to skid so as to close the electric "out-ball" circuit exterior to said line. While clay or wood courts are cited as examples of "skid courts", some degree of skidding is present on all types of surfaces due to the fibrous nature of the tennis ball surface.